Engine systems may be configured with devices such as a throttle turbine generator to harness energy from a pressure difference across a throttle that is otherwise wasted in an intake passage of an engine. For example, the throttle turbine generator may be driven by a pressure difference across a partially open throttle when the engine is run at part load. In some examples, the throttle turbine generator includes a turbine mechanically coupled to the throttle turbine generator which may generate current that is supplied to a battery of the engine. By charging the battery with such a generator, fuel economy of the engine system may be improved.
One example of such an engine system is shown by Leone et al in US20130092125. Therein, a throttle turbine generator is positioned in a throttle bypass. A throttle bypass valve is controlled based on an engine airflow demand to adjust airflow through the throttle turbine generator. Additionally, a throttle position is controlled during engine transients to meet an engine airflow demand.
However, the inventors herein have recognized potential issues with such a system. As one example, when using the pressure difference across the intake manifold to operate the turbine using the throttle, air flow control around the intake manifold becomes more challenging due to continually varying speeds of the turbine and/or generator. In addition, any change to the throttle position simultaneously affects two paths in the intake side of the engine, making airflow control via the throttle challenging. To accurately estimate the airflow, variables such as throttle angle, cross-sectional area of restriction formed by the throttle, pressure difference across the intake manifold and turbine speed may need to be adaptively controlled. As such, to achieve accurate airflow control in view of the multiple variables, one or more four-dimensional performance maps may need to be generated, stored, and accessed quickly. However, generating, storing, and accessing complicated four-dimensional maps may be time, memory, and computation intensive. In particular, besides the complexity of generating and accessing the high-dimensional maps, they may also be prohibitively large to store in an engine controller unit due to memory constraints. As another example, Leone only adjusts the throttle position during transients. However, there may be airflow errors even during steady-state conditions due to variations (e.g., instantaneous) in the speed of the turbine and/or generator.
The inventors have recognized that by learning the pressure difference generated across the intake manifold as a function of throttle angle, at least one two-dimensional map be generated (e.g., in real-time or in advance) and stored in the memory of an engine control unit. Herein, based on each of the pressure difference, and throttle angle, the effective cross-sectional area of the restriction around the throttle may be tabulated. Furthermore, a correction to the effective cross-sectional area of the restriction may be determined by including the effects of turbine speed, for example, which may be stored as a separate two-dimensional map. By performing numerical approximations to the at least two two-dimensional maps, the throttle angle may be accurately determined for effectual airflow control. In addition, from the two two-dimensional maps it may also be possible to accurately predict airflow at a given throttle angle which may then be used for estimating airflow into the manifold for torque monitoring, for example. This results in an approach that is less computation, memory, and time intensive, without compromising on airflow estimation accuracy. Furthermore, the airflow control is performed not just during transient conditions, as shown by Leone et al but during other conditions such as steady-state, idling, etc.
In one example, engine airflow control may be achieved by a method comprising: feed-forward adjusting an intake throttle coupled to a throttle turbine based on driver torque demand; and further adjusting the intake throttle based on each of a first function of a pressure difference across the throttle turbine, and a second, different function of the pressure difference multiplied by turbine speed. In this way, airflow control may be performed accurately and efficiently.
As an example, in response to a driver torque demand, the demanded torque may be delivered from an engine by adjusting a throttle angle of an intake throttle. Since adjusting the throttle angle also adjusts an effective cross-sectional area of a restriction formed by the throttle at an intake pipe, an engine controller may be configured to take into account the impact of the turbine speed on the effective cross-sectional area of the restriction. In particular, the controller may refer to one or more two-dimensional (2D) maps stored in the controller's memory to subtract out this effect, enabling accurate control of air-flow to deliver the demanded torque. For example, the controller may use a first 2D map to learn a first (e.g., initial) adjustment to the position (such as the angle) of the intake throttle based on a first function of a pressure difference across the throttle turbine. Further, the controller may use another 2D map to learn a second, different (e.g., further) adjustment to the position of the intake throttle based on each of the pressure difference across the throttle and a turbine speed of a throttle turbine generator coupled in a bypass across the throttle. As such, the maps may also be used for determining a first airflow amount based on the throttle angle for torque monitoring for example. For example, the controller may use a first 2D map to learn an amount of airflow to the engine based on the position (such as the angle) of the intake throttle based on a first function of a pressure difference across the throttle turbine. Further, the controller may use another 2D map to learn a second, different (e.g., further) adjustment to the airflow amount based on each of the pressure difference across the throttle and a turbine speed of a throttle turbine generator coupled in a bypass across the throttle.
In this way, accurate air flow and torque control may be provided in the presence of an intake throttle turbine and turbine generator. The technical effect of adjusting an intake throttle angle based on a pressure difference across the throttle turbine as well as the turbine speed is that the pressure and airflow effect of the change in throttle angle can be better compensated for. By relying on one or more 2D maps, the airflow control may be performed with increased accuracy without relying on multiple computationally, memory, and time intensive algorithms or maps. In addition, the airflow control can be performed over a wider range of engine operating conditions, including transient and steady-state engine operating conditions. Overall, by improving airflow control, it may be possible to obtain fuel economy benefits while maintaining drivability and emission requirements.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.